Light-matter interactions in optical nanostructures based on organic semiconductors

Abstract

The confinement of a semiconductor material to an optical microcavity leads to an inherent coupling between light and matter. Depending on the lifetime of the excited state of the semiconductor (the exciton) and the cavity photon, two distinct regimes of interaction are possible. The system is said to be weakly coupled if either the exciton or the cavity photon decay before the two species interact. Weak exciton-photon coupling results in a modification of the exciton lifetime, the spectral shape, and the angular dispersion of emission from the microcavity. Conversely, when the lifetimes of the exciton and cavity photon are long enough so that an interaction occurs prior to either state decaying, the regime of strong exciton-photon coupling is realized. The timescale for coupling is the Rabi period, which depends on exciton and cavity parameters including the exciton oscillator strength and transition linewidths. The eigenstates of the strongly coupled system are known as microcavity polaritons. Microcavity polaritons have unique properties arising from their mixed exciton-photon character, permitting the realization of novel optoelectronic devices. Organic semiconductors are attractive for application in strongly coupled systems due to their large exciton binding energy (~1 eV), which permits a robust coupled state that is stable at room temperature and under electrical excitation. In addition, organic semiconductors exhibit large exciton oscillator strengths (~1015 cm-2) resulting in a strong interaction between the cavity photon and the exciton. We aim to better the understanding of polaritons in organic semiconductor microcavities to push the field towards novel optoelectronic devices.